Cardiac patients can have their cardiac activity monitored from a central location via a telephone connection while they remain at home. Such monitoring is particularly useful for patients with implanted heart pacemakers and/or certain heart conditions such as symptomatic arrhythmia episodes. Typically, the patient dials the telephone number of a central monitoring station from a home telephone set, or the center dials the patient's telephone number, to establish a two-way telephone connection over the public telephone switching network. A person at the central station then guides the patient through the steps needed to set up the system for remote monitoring and, when satisfied, asks the patient to place the telephone handset on an acoustic coupler at the home monitoring instrument. A microphone in this coupler is driven by electrical signals supplied to the home instrument over ECG electrode leads, and the sound produced by this speaker in turn drives the telephone handset's microphone which converts it to an electrical analog signal. This analog signal is encoded at the home instrument and sent over the telephone line to the central station for assessment. From time to time, the person at the central station alerts the patient via an alert signal to take some other action. This alert signal may be generated by pushing a number key at the dialing keypad of the dual tone multifrequency telephone set in the central station, and can be used to turn on an indicator light and/or to sound an alarm at the patient's home telephone set.
While such remote monitoring through a home instrument has been useful, it is believed that existing systems still have disadvantages such as critical reliance on the patient to take certain actions in a timely and accurate manner and possible distortion of the data due to interaction in the transmitted signal of pacemaker pulses superimposed on the cardiac electrical activity signal. Inappropriate action on the part of the patient can be a significant problem in this field in view of the age group of the patients that typically use home telephone monitoring of heart and pacemaker function.
An improvement which is believed to improve reliability in some respects is discussed in U.S. Pat. No. 4,938,229 which shares a co-inventor with this application and is hereby incorporated by reference. This improvement has been used for more than a year in this country by the assignee of this invention for remote monitoring of heart and pacemaker function via telephone. U.S. Pat. No. 4,938,229 discusses techniques for encoding ECG and pacemaker data into an FM signal and transmitting the so-encoded data to a central monitoring station for assessment by health care personnel. In addition, other companies are believed to have been involved in supplying equipment for monitoring of heart and pacemaker functions over the telephone. They include Instrumedix in Beaverton, Oreg., Norland Corporation in Fort Atkinson, Wis., Medtronic, Inc. of Minneapolis, Minn., and possibly others.